In conventional optical networks there is always a limit to how far an optical signal can be transmitted along an optical path before the optical signal is lost in optical noise, or before there is sufficient noise to cause intolerable bit errors at the receiver. The target OSNR is the OSNR value at which the receiver reaches the target Bit Error Rate (BER). The OSNR margin, or simply “margin”, is the difference between the estimated OSNR and the target OSNR. In conventional link engineering, the margin has to budgeted in the design phase also taking into account system aging and other unexpected degradation events during the lifetime of the transmission infrastructure. Different physical layer phenomena are taken into account while estimating the margin.